A surprising number of SMTP servers only support port 25 (clear text).

Therefore although the traffic from your email client to your stmp server may be secure, the actual handoff from Server A -> Server B could happen in plaintext. This means that the ISPs involved could read all your emails. (hint hint, they do!)

Having said that most "chat" platforms are owned by big-tech...and SMS is snooped by telecom....so no real privacy there either.